Barriers are divided into three groups, based on the amount they deflect when struck by a vehicle and the mechanism the barrier uses to resist the impact forces. In the United States, traffic barriers are tested and classified according to the AASHTO Manual for Assessing Safety Hardware (MASH) standards. Barrier deflections are related to crash tests with a 2,000 kg (4,400 lb) pickup truck traveling 100 km/h (62 mph), colliding with the rail at a 25 degree angle. Flexible barriers include cable barriers and weak post corrugated guide rail systems. These are referred to as flexible barriers because they will deflect 1.6 to 2.6 m (5.2 to 8.5 ft) when struck by a typical passenger car or light truck. Impact energy is dissipated through tension in the rail elements, deformation of the rail elements, posts, soil and vehicle bodywork, and friction between the rail and vehicle. Semi-rigid barriers include box beam guide rail, heavy post blocked out corrugated guide rail and three-beam guide rail. Three-beam is similar to corrugated rail, but it has three ridges instead of two. They deflect 3 to 6 feet (0.91 to 1.83 m): more than rigid barriers, but less than flexible barriers. Impact energy is dissipated through deformation of the rail elements, posts, soil and vehicle bodywork, and friction between the rail and vehicle. Box beam systems also spread the impact force over a number of posts due to the stiffness of the steel tube. Rigid barriers are usually constructed of reinforced concrete. A permanent concrete barrier will deflect a negligible amount when struck by a vehicle. Instead, the shape of a concrete barrier is designed to redirect a vehicle into a path parallel to the barrier. This means they can be used to protect traffic from hazards very close behind the barrier, and generally require little maintenance. Impact energy is dissipated through redirection and deformation of the vehicle itself. Jersey barriers and F-shape barriers also lift the vehicle as the tires ride up on a angled lower section. The disadvantage of rigid barriers is that there is a high likelihood of rollover. Impact forces are resisted by a combination of the rigidity and mass of the barrier.
For high-speed vehicular traffic, as for instance on a race track special barriers are used to deflect and absorb energy delivered to them. One race track barrier system is defined by U.S. Pat. No. 6,059,487 provides enhanced strength and elasticity for absorbing greater energy during impacts without causing permanent damage to either the vehicle or the barrier, and also provides enhanced properties for redirecting a vehicle during impact. Furthermore, it can be easily assembled in the field from a few, basic, light-weight components. It can also be configured in almost any shape, and is easily reconfigured or, in the case of impact, restored to its original position. Thus, it is well suited to racing tracks, where it is able to be relatively easily laid out, restored and reconfigured. A barrier system according to the present invention is formed from a plurality of barrier modules pivotally linked together to form a barrier chain. Each barrier module can be assembled from a few basic components. These components include an elastically or resiliently deformable barrel rotatably mounted between a pair of links. The barrel is journailed on a pin that extends between the pair of links. This same pin can be used to pivotally connect two modules by overlapping end portions of the links from the respective modules. Each module further includes a spacer between the pair of links. The spacer maintains separation between the links so that the barrel is free to rotate. Furthermore, the spacer is structurally joined with the top and bottom links to create a rigid structure when the module is assembled. The resulting structure thus tends to resist twisting. The chain of barrier modules may be anchored by one or more of the pins extending into bore holes in the ground or a footing.
A further race track barrier system is defined by U.S. Pat. No. 6,702,513 wherein a smooth wall is hinged or pivoted at its bottom edge and is able to move to an upright position against a crushable material positioned behind the wall thereby absorbing the energy of a crashing vehicle. The wall extends outwardly toward the track so that vehicles tend to be prevented from leaving the road surface. The barrier defined herein is primarily designed to protect spectators when high speed racecars crash at very high speed and often have enough kinetic energy to leave the racing surface.